Production of fine fibrous structures

ABSTRACT

AN AQUEOUS EMULSION CONTAING A LINEAR POLYMER AND A SOLVENT POSITIVE RELATIVE TO THE POLYMER IS EJECTED FROM A REGION AT A TEMPERATURE HIGHER THAN THAT AT WHICH THE POLYMER IS AT LEAST CAUSED TO SWELL IN THE EMULSION BUT LOWER THAN THE CRITICAL TEMPERATURE OF THE EMULSION, AND AT A PRESSURE HIGHER THAN THE SATURATED VAPOR PRESSURE OF THE EMULSION, INTO A LOW-PRESSURE REGION AT A TEMPERATURE AND PRESSURE ENABLING THE LIQUID PHASE WHICH HAS INFILTRATED INTO DROPLETS OF THE POLYMER IN THE EMULSION TO VAPORIZE, THEREBY PRODUCING A FINE FIBROUS STRUCTURE. THE WEIGHT RATIO OF THE SOLVENT TO THE POLYMER IS GREATER THAN UNITY, AND THE DROPLETS CONTAIN A WATER-SORPTION AGENT IN A QUANITY OF FROM ZERO TO 80 PRECENT OF THE WEIGHT OF THE POLYMER.

United States PatentO 3,770,856 PRODUCTION OF FINE FIBROUS STRUCTURES Shiro Ueki and Tadayuki Fnkada, Yokkaichi, Japan, as-

signors to Kabushiki Kaisha Oji Yuka Goseishi Kenkyujo, Tokyo-to, Japan No Drawing. Filed Sept. 3, 1971, Ser. No. 177,865 Claims priority, application Japan, Sept. 8, 1970, 45/755,156 Int. Cl. B29c 23/00 US. Cl. 26413 Claims ABSTRACT OF THE DISCLOSURE An aqueous emulsion containing a linear polymer and a solvent positive relative to the polymer is ejected from a region at a temperature higher than that at which the polymer is at least caused to swell in the emulsion but lower than the critical temperature of the emulsion, and at a pressure higher than the saturated vapor pressure of the emulsion, into a low-pressure region at a temperature and pressure enabling the liquid phase which has infiltrated into fluid droplets of the polymer in the emulsion to vaporize, thereby producing a fine fibrous structure. The weight ratio of the solvent to the polymer is greater than unity, and the droplets contain a water-surption agent in a quantity of from zero to 80 percent of the weight of the polymer.

BACKGROUND This invention relates generally to the production of fine fibrous structures and more particularly to a new process for producing fine fibrous structures for providing fine fibers suitable for use as a starting material in the making of synthetic papers.

As one class of synthetic paper, papers of a structure comprising an intertwinement of fibers are known. A paper of this class is made by using fibers of a synthetic polymer as one ingredient of a natural cellulosic papermaking material or in place thereof.

A synthetic paper of this class is advantageous in that its structure is essentially the same as that of conventional or natural papers. However, fibers for synthetic papers are required to have a high degree of molecular orientation, to be thin, and to have a highly fibrillated structure, and synthetic polymeric fibers which have been generally used for fabrics and clothing are accompanied by difliculties with respect to these requirements. Furthermore, synthetic polymeric fibers of this character have poor hydrophilic property. For these reasons, satisfactory synthetic papers of this class have not been available.

On one hand, one known method for producing fine fibers usable as fibers for synthetic papers of this character comprises abruptly ejecting or jetting a solution of a crystalline polymer under pressure and at a temperature above room temperature through orifices into a low-pressure region and thereby recovering the polymer as a fine fibrous structure together with the resulting evaporation of the solvent used. By macerating or beating the fine fibrous structure thus obtained by this spinning method, fine fibers of fibrillated structure having ample fineness and ample strength due to molecular orientation can be obtained. By using these fine fibers in paper making, it is possible to produce a synthetic paper which even more closely resembles conventional paper.

Fine fibers of this character and the method for promust have a low'boiling point, and, moreover, a large quantity of the solvent must be used. Furthermore, fine 3,770,856 Patented Nov. 6, 1973 fibers produced in this manner lack hydrophilic property, whereby making papers therefrom is not always easy.

SUMMARY It is an object of this invention to solve the above described problems in providing a relatively simple process for producing fine fibrous structures. We have found that this object can be achieved by ejecting into a low-pressure region a liquid in the form of a pressurized aqueous emulsive liquid containing a linear polymer.

According to this invention, briefly summarized, there is provided a process for producing fine fibrous structures which comprises ejecting an aqueous emulsive liquid containing a linear polymer from a high-pressure region into a low-pressure region, in which process: (l) The emulsive liquid comprises from 5 to 40 percent by weight of the polymer, from 10 to percent by weight of a positive solvent, the Weight ratio of the solvent to the polymer being greater than one (unity), and from 10 to 80 percent by weight of water;

(2) The high-pressure region is at a temperature higher than that at which the polymer is at least caused to swell in the liquid by, the action of the solvent, but lower than the critical temperature of the liquid, and at a pressure higher than the saturated vapor pressure of the liquid, the polymer thereby being in the form of fluid droplets in the liquid in the high-pressure region, these droplets containing a liquid phase which has infiltrated thereinto;

(3) The low-pressure region is at a temperature and pressure enabling the liquid phase in the droplets to evaporate; and

(4) The droplets contain therewithin a water-sorption agent in a quantity of from zero to 80 percent of the quantity of the polymer.

The nature, utility, and further features of. this invention will be apparent from the following detailed description beginning with a consideration of general aspects of the invention and concluding with specific examples of practice illustrating preferred embodiments of the invention.

' DETAILED DESCRIPTION in accordance with this invention, an aqueous emulsive liquid is used for the spinning solution of the polymer to be spun by ejecting it into a low-pressure region. We have found that by the process of this invention, the following desirable eifects and features are attainable.

(l) Blowing elfects Two kinds of blowing effects, that of water and that of the solvent are utilized. The mode of utilization difiers depending on the difierence between the vapor pressures of the solvent and water. That is, in the case where the solvent used together with water has a lower boiling point than water, the principal blowing agent is the solvent. On the other hand, in the case where a solvent of a higher boiling point than water is used together therewith, the water is the principal blowing agent.

The water and solvent which have infiltrated into the interior of the polymer fluid droplets which have at least swelled because of the solvent, that is, the positive solvent (described in detail hereinafter), are subjected to a sudden release of pressure and undergo an instantaneous or flash evaporation to produce a blowing eflect when the polymer emulsive liquid is ejected in the low-pressure regionfiThis sudden pressure release is accompanied by an abrupt cooling, whereby the polymer is simultaneously blown and cooled.

(2) Molecular orientation eifect Two sources of water may be considered to exist in the polymer emulsive liquid, namely, the water which has infiltrated into the polymer droplets and the water which has not infiltrated into the polymer droplets.

The latter water evaporates at the instant at which the polymer emulsive liquid is extruded or ejected into the low-pressure region and, becoming a current of steam, is directed with extremely high energy in the ejection direction. This steam current has the effect of exerting a powerful stretching force on the polymer in the ejected direction.

While the polymer is rapidly cooled from its interior and exterior parts by the abrupt evaporation of the solvent within the polymer droplets and the water within and outside of the droplets, these actions of blowing, stretching, and cooling take place substantially simultaneously. For this reason, a. structure comprising fine fibers having a high degree of molecular orientation and, moreover, a high degree of fibrillation can be obtained.

(3) Hydrophilic property In accordance with a preferred mode of practice of this invention, an emulsifier is used in order to prepare a stable polymer emulsive liquid.

This emulsifier remains within the polymer after the Water has evaporated in the low-pressure region. Accordingly, the fine fibrous structure obtained in this case is highly hydrophilic and sufficiently dispersible in water even without the addition of any dispersing agent. Furthermore, there is no problem such as foaming. Accordingly, the fibrous structure can be readily sent to the succeeding maceration or beating and paper-making steps. Furthermore, synthetic papers having good water wetting property, which was unattainable by the prior art, can be produced.

(4) Expansion of the range of usable solvents By the flash spinning techniques known heretofore, solvents of high boiling points could not be used because of difiiculties relating to the blowing properties and to the removal of the residual solvent.

By the practice of this invention, however, these highboiling-point solvents can also be used. Even if a highboiling-point solvent remains within the product polymer, it can be removed in a relatively easy manner by washing the product with water containing an emulsifier. The emulsion formed during this washing process and containing a small quantity of a solvent can be effectively utilized as a starting material for preparing the polymer emulsive liquid.

(5) Reduction of solvent used The fluidity necessary for ejecting the emulsive liquid through orifices can be attained by the action of the water which does not infiltrate into the interior of the polymer droplets. Furthermore, it is possible to replace the solvent contributing to blowing with the water which has infiltrated into the interior of the polymer droplets. Moreover, since the water and the solvent are immiscible, the dissolving capacity of the solvent does not decrease, whereby it is possible to reduce, relatively, the quantity of the solvent with respect to the polymer.

The most unique feature of this invention is the fact that a blowing agent for the polymer is water. This feature is extremely suitable for the production of fine fibers of high orientation, particularly fibers of diameters of the order of 5 microns and lengths of the order of from 2 to 5 mm.

The production of highly orientated fine fibers by ejecting a polymer containing a blowing agent and existing substantially in a fluid state into a low-pressure region depends on the following requisite factors.

(a) REALIZATION OF STRETCHING AND ORIENTATION (a-l) Blowing capacity (i) Quantity of blowing agent.A large quantity is desirable. Therefore, the blowing agent should be in liquid form.

4 (ii) Expansibility.A high expansibilit is desirable. Therefore, the blowing agent should have a low molecular weight and a low boiling point.

( 21-2) Stretchability (i) Momentum.A large momentum is desirable. Therefore, the blowing agent should be one having a high specific gravity.

(ii) Interfacial relationship.--The wetting of the polymer by the blowing agent should be good at the interface therebetween.

(b) FIXING THE ORIENTATION (b4) Latent heat of vaporization For rapid cooling of the molten polymer, the latent heat of vaporization of the blowing agent should be great.

(b-2) Joule-Thomson effect For the same reason, the Joule-Thomson effect should be appreciable during the evaporation of the blowing agent.

We have found that the blowing agent which most fully satisfies these various requirements is water, particularly water combined with a positive solvent with respect to the polymer and/ or a surfactant.

Linear polymer.For the polymer to be used in accordance with this invention to achieve the desirable features enumerated hereinabove, in general, any linear polymer capable of forming fibers can be used.

For producing ample molecular orientation effect, a crystalline polymer is preferable. Furthermore, in view of the fact that this polymer is often subjected in the state of an aqueous emulsive liquid to pressure and heat, and in consideration of hydrolysis which may occur, a polymer prepared by polyaddition is more preferable, if a choice must be made, than a polymer prepared by polycondensation.

Examples of such linear polymers are polyolefin resins, polychloroethylene resins, aromatic polyvinyl resins, polyacrylic resins, polyamide resins, polyimide resins and polyester resins, as homopolymers or as copolymers. Of these resins, the most representative are polyolefin resins. Of these, furthermore, isotactic polypropylene and highdensity polyethylene are most representative. These resins can be used singly or as mixtures thereof.

Positive solvent.--A positive solvent is used for transforming the above defined linear polymer into the form of an aqueous emulsive liquid. The term positive solvent is herein used to designate a solvent which has a positive characteristic with respect to the given linear polymer, that is, is capable of causing the polymer to swell or dissolve under the temperature and pressure conditions of the high-pressure region." Accordingly, the positive solvent may have, although it need not have, this positive characteristic in a low-pressure region or under the conditions of room temperature and atmospheric pressure.

Since this positive solvent is to be used for preparing an aqueous emulsive liquid of the polymer, it should be a solvent which is substantially immiscible with water, except for a solvent having a positive characteristic as mentioned above in the form of an aqueous solution, and inert with respect to the polymer. Specific examples of this positive solvent are aliphatic hydrocarbons, alicyclic hydrocar bons, aromatic hydrocarbons, and halogenated hydrocarbons, which are used singly or as mixtures thereof.

Emulsifier and other adjuvants.-In accordance with a preferred embodiment of this invention, an emulsifier is used to prepare the aqueous emulsive liquid. For the emulsifier, any emulsifier which is capable of producing a stable emulsive liquid in the high-pressure region can be used.

Accordingly, a suitable emulsifier can be selected from those generally sold on the market. Specific examples are surface-active agents of the non-ionic class, the anionic class, the amphoteric ionic class, and the zwitter ionic class, which may be used singly or as mixtures thereof. The aqueous emulsive liquid comprising, indispensably, water, a positive solvent, and a linear polymer may contain other auxiliary ingredients as required. For example, in addition to the above mentioned emulsifier, watersoluble salts, water-soluble polymers, and other additives can be added to adjust properties of the emulsive liquid such as its viscosity and stability. When a water-soluble is used, it may be removed by washing from the resulting fine fibrous structure, or it can be rendered insoluble in water. Furthermore, a fine filler, a foaming agent, and other adjuvants canbe added.

Water-'sorption agent-One example of modification of the polymer aqueous emulsive liquid of the above described character is the introduction thereinto of a watersorption agent for promoting the infiltration of water into the interiors of the polymer droplets. That is, the substance which acts as a blowing agent in the practice of this invention is the water which has infiltrated into the interior of the liquid droplets of the polymer which is in solution or swollen, together with the positive solvent.

Accordingly, if a large quantity of the water infiltrates into the polymer liquid, the blowing effect will be great, and the fine fibers obtained will have improved stiifness. From this standpoint it is desirable to cause a hydrophilic water-sorption agent to exist within the polymer liquid droplets thereby to utilize the water-retaining property thereof.

This water-sorption agent may be an inorganic or organic material soluble in water or a material which is insoluble in water but is water sorptive.

Examples of the former are inorganic materials such as nitrates, sulfates, phosphates, carbonates, organic acid salts, hydroxides, and halides of alkali metals, alkaline earth metals, aluminum, and ammonia, and complex salts and double salts thereof, specific examples being NaNO Na CO NaCl, NaH PO MgSO CH COONa, NaOH, and (NH )Al(SO Further examples of the former are organic substances such as carboxymethylcellulose, agar, and polyvinyl alcohols.

Examples of the latter are water-insoluble materials such as calcium carbonate, white carbon, clays, basic magnesium carbonate, diatomaceous earth, cellulose powders, and pulps and materials which are difiicult to dissolve in water such as magnesium oxalate and magnesium phoshate.

P These water-sorption agents are used in an amply fine state of an average particle diameter of the order of, for example, from 1 to 2 microns. A water-sorption agent of this character can be caused to be present within the polymer fluid droplets by any suitable method. One such method is to knead this agent beforehand with the polymer. In the case where this water-sorption agent is waterinsoluble or dissolves with difficulty in water, it can also be added at the time of preparation of the polymer emulsive liquid.

Composition of the aqueous emulsive liquid-The aqueous emulsive liquid according to this invention must be of a specific composition.

First, the polymer concentration will be considered. If the concentration within the emulsive liquid is less than 5 percent, it is practically meaningless on the point of productivity, and, moreover, the preparation of an emulsive liquid of uniform dispersion is difficult. On the other hand, a concentration of more than 40 percent results in difficulty in attaining a uniform dispersion within the emulsive liquid, and, at the same time, the polymer does not assume a state of uniform and good fibrillation Accordingly, the range of suitable polymer concentration is from 5 to 40 percent, preferably from to 30 percent.

While water and the solvent each exist in a proportion of from 10 to 80 percent, preferably from 20 to 60 percent, the ratio of the solvent to the polymer is made greater than one (unity), preferably from 1.5to 6, in order to cause the water to emulsify and infiltrate amply into the polymer which has been swollen or dissolved by the solvent and to cause the polymer to assume a fully fibrillated state.

The emusifier content is of the order of less than a few percent. In one example of the case where a high-density polyethylene (density of the order of 0.95 gram/cc. or higher) is used as the linear polymer, the polymer concentration is of the order of from 10 to 30 percent, the positive solvent concentration is of the order of from 30 to 60 percent, and the water content is of the order of from 20 to 50 percent. In the case where a hydrophilic material is to exist within the polymer liquid droplets as mentioned hereinbefore, the quantity thereof is from 0 to percent, preferably from 30 to 50 percent by weight.

Spinning.The high-pressure region wherein the aqueous emulsive liquid of this character initially exists should be at a temperature sufiicient for full exhibition of the positive characteristic of the solvent. Furthermore, since the emulsive liquid should exist as a liquid, the pressure should be above the saturated vapor pressures at that temperature of water and the solvent.

Furthermore, since the blowing action of water is principally utilized in the practice of this invention, the temperature and pressure conditions of the high-pressure region are selected with respect to their relationships with the pressure and temperature conditions of the lowpressure region. Accordingly, in the case Where the low-pressure region is at atmospheric pressure, the blowing action of the water does not become sufiicient at a temperature of the high-pressure region of less than C. In order to apply or sustain this pressure condition in the high-pressure region, a pressure-applying means can be resorted to. However, the ordinary method is to introduce a pressurized gas, which is preferably inert with respect to the aqueous emulsive liquid.

One example of the conditions of the high-pressure region is that wherein, in the case of ejection of a highdensity polyethylene aqueous emulsive liquid of the aforementioned composition into a low-pressure region at atmospheric pressure, for example, the temperature is of the order of from to 200 C., and the pressure is of the order of 40 kg./cm. or higher.

The extrusion or ejection of the aqueous emulsive liquid of the polymer from the high-pressure region to the low-pressure region may be carried out through an ejection orifice device which has a single hole, a plurality of holes, or holes of slit shape or some other shape. We have found that, while an ejection velocity from the ejection orifice device is preferably above the Velocity of sound (330 meters/second), a velocity of approximately one-half of the velocity of sound or lower velocity may be used.

While, the low-pressure region is ordinarily at atmospheric pressure and room temperature, it is also possible to maintain this region under reduced pressure and heated conditions in' order to promote the evaporation of the liquidphase, particularly water, within the emulsive liquid.

Product-The fine fibrous structure thus obtained is dried directly as it is or is washed with an aqueous solution of an emulsifier and then dried, whereupon the objective product is obtained.

This fine fibrous structure can be utilized as a network structure. By macerating or beating this fine fibrous structure by a dry or wet process, it can be also utilized as staple fiber or as a starting material for paper making. As mentioned before, according to a preferred embodiment of this invention, there is provided fine fibers of good hydrophilic characteristics which are particularly excellent for use as starting material for paper making and, moreover, have excellent compatibility with natural cellulosic pulp. In order to indicate still more fully the nature and utility of this invention, the following specific examples of practice constituting preferred embodiments of the invention and results are set forth, it being understood that these examples are presented as illustrative only, and that they are not intended to limit the scope of the invention.

EXAMPLE 1 To 25 parts of water, one part of a non-ionic emulsifier of HLB=7 is added and dissolved therein. As the result ing mixture is agitated, 59 parts of n-pentane is added, whereupon a uniform emulsion is obtained. To this emulsion, 15 parts of a linear polyethylene powder of a MI of is added and uniformly dispersed.

The resulting mixture is placed in a sealed vessel, which is then pressurized to 30 kg./crn. with pressurized nitrogen. Then, as the mixture is agitated, it is heated to 150 C. After one hour, the pressure within the vessel is raised to 46 kg./om. by raising the temperature. The sealed vessel is communicative through a gate valve to slit nozzles of a width of 0.5 mm. and a length of mm.

After one hour, the pressure within the sealed vessel is raised further to 70 kg./cm. with pressurized nitrogen. Then, by suddenly opening the gate valve, the process mixture is ejected through the slit nozzles and into the atmosphere.

As a result, in one instance of practice, a three-dimensional network structure of high degree of orientation was produced. The ejection velocity in this instance was 9,000 meters/minute. The network structure thus produced was macerated for minutes in a mixer, whereupon fine flat fibers in fibrillar state of an average width of from 5 to 10 microns and lengths of from 3 to 5 mm. were obtained.

As a result of microscopic examination, these fibers were found to have a configuration which was almost the same as that of wood pulp. These fibers were further found to have excellent hydrophilic property and to have, in their original state, high dispersibility in water.

These fine fibers were made into a paper by means of a manually-scooping paper-making machine and pressed for 3 minutes at C. and under a pressure of 60 kg./ cm. whereupon a synthetic paper of a thickness of 100 microns and a density of 0.35 gram/cc. having ample opacity and excellent writability was produced. It was found further that this paper had very good water wettability.

EXAMPLE 2 In 45 parts of water, one part of a non-ionic emulsifier of HLB=18 is added, and, as the resulting solution is agitated, 44 parts of xylene is added thereto to prepare a uniform emulsion. To this emulsion, 10 parts of a liner polyethylene powder of a MI of 5 is added and uniformly dispersed. The resulting mixture is placed in the sealed vessel specified in Example 1, the interior pressure of which is raised with nitrogen under pressure to 25 kg/ cm.*. The process mixture is thus heated to 180 C. as it is agitated. In one instance of practice, the vessel pressure rose to 42 kg./em. after 40 minutes of his heating and agitating.

In this instance, the vessel pressure was further raised to 45 kg./cm. with nitrogen pressure. The gate valve was then opened to eject the process mixture into the atmosphere, whereupon a three-dimensional network structure having fine gas bubbles was obtained. This structure was immediately immersed in water containing an emulsifier and agitated thereby to remove residual xylene. The structure was further washed twice with water and then macerated for 15 minutes in a mixer, whereupon fiat fine fibers in fibrillar state of an average width of from 10 to 15 microns and lengths of from 3 to 5 mm. were produced.

These fibers were made into a paper by means of a manually-scooping paper-making machine, whereupon a synthetic paper having excellent water wettability and excellent writability was obtained.

8 EXAMPLE 3 15 parts of a linear polyethylene of a MI of 5 was added to an emulsion comprising 42 parts of water, 42 parts of n-pentane, and one part of a non-ionic emulsifier of HLB-=11. The resulting mixture was subjected at 135 C. to the process set forth in Example 1, whereupon a three-dimensional network structure of a. high degree of orientation was obtained.

The structure was beaten with a single-disk refiner, whereupon fiat fine fibers in fibrillar state of an average width of from 5 to 10 microns and lengths of from 2 to 3 mm. were produced.

Furthermore, a PEI mill was used to carry out heating for 20 minutes under the conditions of a concentration of 10 percent, a load of 3.4 kg, a rotational speed of 2,400 r.p.m., and a clearance of 1 mm. As a result, fine fibers of an average width of from 15 to 25 microns and lengths of from 3 to 7 mm. were produced. It was found that these fine fibers were substantially equal in quality to fine fibers obtained by macerating the network structure with a mixer having blades rotating at 10,000 r.p.m., and that these fibers could be used advantageously in making synthetic papers.

EXAMPLE 4 In 47 parts of water, 0.5 part of an anionic surfactant was dissolved, and the resulting solution was heated to C. Separately, 5 parts of a linear polyethylene was dissolved at C. in 47 parts of tetralin, and the resulting solution was added by dropping in the above mentioned solution heated to 90 C. The solution thus obtained was processed in a Homomixcr Operated at a high speed of 10,000 r.p.m. thereby to prepare an emulsive polymer liquid.

This liquid was heated and mixed for 40 minutes at a temperature of C. under a pressure of 40 kg./cm. in the vessel specified in Example 1 and was then ejected into the atmosphere through nozzles of 10-mm. length and l-mm. width, whereupon a three-dimensional structure was obtained. This structure was found to have a substantially advanced state of fibrillation, but had a considerable quantity of residual Tetralin.

This structure was irmnediately macerated for 15 minutes together with water containing an emulsifier in a mixer and then washed twice with water to remove the Tetralin. As a result, flat fine fibers in fibriliar state of an average width of from 10 to 15 microns and lengths of from 2 to 3 .mm. were produced. These fibers were found to be highly suitable for use in making synthetic papers.

EXAMPLE 5 In an emulsive liquid comprising 42 parts of water, 42 parts of n-heptane, and one part of an anionic surfactant, 15 parts of an isotactic polypropylene in powder form of a MI of 9 was uniformly dispersed. The mixture thus prepared was heated for 40 minutes at 180 C. as it was agitated in a sealed vessel under a pressure of 25 kg./ 0111. Thereafter, the pressure within the vessel was raised to 40 kg./cm.

The pressure was then raised further with nitrogen under pressure to 50 kg./cm. and the mixture was discharged in one operation through the slit nozzles specified in Example 1 into the atmosphere, whereupon a continuous three-dimensional network structure having a high degree of orientation was obtained. This structure was macerated for 15 minutes in a mixer. As a result, flat fibers of an average width of from 10 to 15 microns and lengths of from 3 to 5 mm. were obtained. These fibers were found to have substantially the same configuration as that of wood pulp.

These fibers were used in making paper by means of a manually-scooping paper-making machine, being pressed under a pressure of 70 kg./cm. whereupon a synthetic paper suitable for practical use of high opacity and excellent writability was obtained. This synthetic paper was further found to have an extremely good water wettability.

EXAMPLE 6 One part of an anionic surfactant was dissolved in 69 parts of water. Then, as the resulting solution was agitated, 20 parts of toluene was added thereto to prepare a uniform emulsive liquid. To this liquid, 10 parts of a polyvinyl chloride powder was added thereby to prepare a uniform dispersed mixture.

This mixture was placed in the sealed vessel specified in Example 1 and, as it was agitated, was left for 40 minutes at 140 C. and under a pressure of 25 kg./cm. whereupon the pressure within the process system rose to 37 kg./cm. The pressurewas further raised to 40 kg./cim. with pressurized nitrogen. The process mixture was then ejected in one operation through the nozzles of Example 1 into the atmosphere, whereupon a three-dimensional network structure similar to that of high-density polyethylene was obtained.

EXAMPLE 7 One part of an anionic surfactant was dissolved in 39 parts of water. As the resulting solution was agitated, 30 parts of n-pentane was added thereto to prepare an emulsion. To this emulsion 30' parts of a linear polyethylene of a MI of 5 in powder form was added and uniformly dispersed therein. The resulting mixture was placed in the sealed vessel of Example 1 and, under a pressure of 30 kg./cm. was heated to 180 C. as it was agitated. After one hour, the process system pressure was raised to 50 kg./cm.

The pressure was further raised to 55 kg./cm. with pressurized nitrogen, and the process mixture was ejected through the nozzles of Example 4 into the atmosphere thereby to accomplish fibrillation thereof.

The fine fibrous structure thus obtained was found to be a three-dimensional network structure of a form made up of a collection of several net-like structures, and lumps of foamed structural state of partially insufficient fibrillation were found therein.

This structure was macerated for 15 minutes in a mixture, whereupon flat fine fibers of an average width of from 20 to 30 microns and lengths of from 3 to 7 mm. were produced. These fibers were used in making a paper, whereby a synthetic paper of excellent writability was obtained.

EXAMPLE 8 70 parts of a linear polyethylene and 30 parts of an isotactic polypropylene were roll kneaded for 10 minutes at 190 C., and then ground in a mill to a powder of an average particle diameter of 500 microns. 15 parts of this powder was added to an emulsive liquid previously prepared from 42 parts of water, 42 parts of n-heptane, and one part of an anionic surfactant thereby to form a mixture liquid.

This mixture liquid was heated and mixed for one hour at a temperature of 180 C. and under a pressure of 50 kg./cm. in accordance with the procedure set forth in Example 1 and then ejected into the atmosphere. As a result, a three-dimensional network structure fibrillated to a high degree similarly as in Example 1 was obtained.

EXAMPLE 9 A uniform dispersion mixture liquid was prepared by adding 15 parts of a powder of an ethylene-propylene cpolymer (C content of percent by weight) of a MI of 0.8 to an emulsive liquid comprising 34 parts of water, 50 parts of n-hexane, and one part of a surfactant of HLB=10.7. This mixture liquid was extruded into the atmosphere by the procedure set forth in Example 1, whereupon a similar three-dimensional network structure was produced.

, 10, EXAMPLE 10 To 50' parts ofa linear polyethylene of a MI of 5, 20 parts of a polystyrene, 10 parts of magnesium sulfate, 10 parts of calcium carbonate, and 10 parts of a clay were added, and the resulting mixture was roll kneaded for 10 minutes at C. and pelletized. The pellets thus formed were then ground to form a powder of an average particle diameter of 200 microns.

30 parts of this powder was uniformly dispersed in a previously prepared emulsion comprising 40 parts of n pentane, 29 parts of water, and one part of a non-ionic anionic surfactant. The resulting mixture was placed in a sealed vessel, the interior pressure of which was then raised to 30 kg./cm. with pressurized nitrogen, and the mixture was heated at C. while being agitated. After one hour, the interior pressure of the vessel was increased further with pressurized nitrogen to 75 kg./cm. and the process mixture was ejected into the atmosphere through slit nozzles each of 0.5-mm. width and l0-mm. length, whereupon a group of fine fibers similar to that of Example l was obtained.

These fibers were beaten by means of a single-disk refiner. As a result, flat fine fibers in fibrillar state of an average width of from 5 to 10 microns and lengths of from 3 to 5 mm. were obtained.

We claim:

1. A process for producing fine fibrous structures which comprises preparing an aqueous emulsive liquid containing from 5 to 40% by weight of a linear polymer, from 10 to 80% by weight of a positive solvent which is substantially immiscible with water, the weight ratio of solvent to polymer being greater than one, and from 10 to 80% by weight of water, subjecting the liquid to a pressure higher than the saturated steam pressure of the liquid and a temperature higher than that at which the polymer is at least caused to swell in the liquid by the action of the solvent, but lower than the critical temperature of the liquid, thus causing formation in the liquid of fluid polymer droplets containing a liquid phase which has infiltrated into the droplets, and ejecting the liquid containing the droplets into a low-pressure region at a temperature and pressure enabling the liquid phase in the droplets to evaporate, thereby splitting the fluid polymer into fine fibrous structures.

2. A process according to claim 1 in which the linear polymer is a polyolefin selected from the group consisting of homopolymers and mutual copolymers of ethylene propylene, and butene-l, copolymers of said monomers as predominant constitute constituents with other monomers copolymerizable therewith, and mixtures of said polymers.

3. A process according to claim 2. in which the linear polymer is a mixture of said polyolefin and a polystyrene.

4. A process according to claim 1 in which the linear polymer is a polyvinyl chloride.

5. A process according to claim 1 in which the linear polymer is a member selected from the group consisting of polyethylenes, isotactic polypropylenes and mixtures thereof, and the positive solvent is a member selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons and aromatic hydrocarbons.

6. A process according to claim 5 in which the emulsive liquid also contains a non-ionic surfactant.

7. The process according to claim 1 in which the positive solvent is a member selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons and mixtures thereof.

8. The process according to claim 1 in which the fluid polymer droplets contain up to 80% by weight, based on the weight of the polymer, of a water-sorption agent.

9. A process according to claim 8 in which the watersorption agent is a fine solid selected from the group consisting of nitrates, oxalates, acetates, sulfates, sulfites,

1 1 carbonates, phosphates, hydroxides and halides of alkali metals, alkaline earth metals and ammonium.

10. A process according to claim 8 in which the watersorption agent is a fine water-insoluble solid comprising a silicate.

References Cited UNITED STATES PATENTS 3,081,519 3/1963 Blades et al. 264-209 3,227,794

1 2 FOREIGN PATENTS 789,079 7/1968 Canada 264-12 LEWIS T. JACOBS, Primary Examiner U.S. Cl. X.R.

1/1966 Anderson et al. 264-205 10 2 0 33 5 341; 2 4 205 

